甲烷二氧化碳重整高稳定性镍基催化剂的重新构建

Sintering of Ni nanoparticles and formation of coke are two important issues for Ni-based catalysts during CO2 reforming of methane. In this project, MgAl2O4 encapsulated Al2O3 support will be designed and synthesized by enhanced interfacial defects in Al2O3 at low temperatures, which is then used to fabricate novel Ni-based catalyst with high efficiency and strong resistance to sintering and coke. Owing to the large surface area, this encapsulated support can be employed to generate highly dispersed Ni nanoparticles and suppress the formation of inactive NiAl2O4, which improves the utilization of metal active sites. Furthermore, the strong metal-support interaction is favor of stabilizing and anchoring Ni nanoparticles on the support, leading to an improved anti-sintering property of novel catalyst. Simultaneously, by tuning the distribution of Lewis basicity and acidity on the catalyst along with the introducing promoters, the CO2 adsorption capacity and activation ability are enhanced, which facilitate the conversion of intermediate carbon species, contributing to a high anti-coke performance over the novel catalyst. The relationship between the interaction of support, Ni, and promoter and the anti-sintering and anti-coke property of the catalyst in CO2 reforming of methane will be discussed systematically. This gives a guidance to the growth and aggregation of Ni nanoparticles and evolution of coke formation on the catalyst during the reaction. It is expected that the project can provide a new route for the preparation, development and industrial application of novel Ni-based catalysts with high resistance to sintering and coke.

本项目针对甲烷二氧化碳重整催化剂中镍纳米颗粒烧结和积碳等瓶颈问题，在设计镍铝催化剂的过程中，提出了缺陷位诱导低温合成MgAl2O4包覆Al2O3载体，制备高效且具有高抗烧结和抗积碳性能的新型镍基催化剂。该思路利用了包覆型载体高比表面积和介孔特性，在提高镍纳米颗粒分散性的同时抑制非活性NiAl2O4的产生，且通过增强镍-载体相互作用力，稳定高分散镍纳米颗粒，改善其抗烧结性能。同时，通过调控包覆型载体表面酸碱性分布及添加助剂，增强催化剂的CO2吸附和活化能力，促进干重整反应中含碳物种的转化，提高新型催化剂的抗积碳性能。通过深入研究催化剂中载体-镍-助剂三者协同作用机制与其抗烧结和抗积碳性能的关系，揭示反应过程中镍颗粒团聚、生长过程和碳物种的演变规律。本项目的实施可为抗烧结和抗积碳新型结构镍基催化剂的研制、开发和工业应用提供新的路径。

甲烷干重整是制取CO和H2合成气等下游工业必需品的过程，负载型镍基催化剂价格低廉、来源广泛，具有与贵金属媲美的性能成为干重整反应研究焦点。然而，由于镍颗粒较高的积碳化学势和较低的塔曼温度，使其在反应过程中面临着积碳和烧结所引起的失活。因此，开发高抗积碳和高抗烧结的镍基催化剂是其实现干重整应用的关键。工业常用镍铝催化剂，强化金属与载体间的相互作用力能够稳定镍纳米颗粒，而过强的相互作用力易导致非活性NiAl2O4的形成，降低催化反应性能。通过本项目的实施，申请人提出了：1）精准调控金属镍与助剂CeO2两者间相互作用力，在避免非活性NiAl2O4产生的同时，增强了镍与CeO2间距离效应、界面效应；促进且匹配Ni/CeO2–SiO2、Ni/CeO2–Al2O3催化剂上CH4和CO2分子的吸附与活化（形成HCOO–物种），构建碳沉积与碳消除的动态平衡机制，有效抑制了石墨碳物种的形成（以活泼碳物种和低石墨化的无定型碳为主），提高了干重整反应的抗积碳能力；2）合理调变载体微环境（官能团和配位情况），在改变镍颗粒落位效应（载体内部和表面）的同时，通过限制Si–H官能团水解与缩合反应或丰富的五配位Al3+结构，构筑限域结构以稳定纳米镍颗粒；实现其在强放热反应体系下对CO和CO2分子的高效活化和高选择性转化，中等强度作用于载体（硅氧烯、Al2O3）内部的镍颗粒反应条件下缓慢释放，增强了其高温反应的抗烧结能力；3）定向降低Al2O3载体结晶度，获得高比面积镍铝催化剂（200 m2 g–1）且极大抑制了NiAl2O4的形成（无定型Al2O3）的同时，通过金属与金属（镍铁、镍锌、镍钴）、金属与载体间作用力的合理强化，较好地稳定了镍和镍合金颗粒，提升了镍系催化剂对CO2的活化和对低石墨化碳物种的转化能力，其中原位反应合成核壳结构Ni3ZnC0.7/Al2O3催化剂有效抑制了积碳的形成（积碳速率为0.003 mgc gcat–1 h–1），促进了干重整反应活性和抗积碳性能。围绕上述研究内容，本项目执行期间受邀撰写RSC Catalysis第二章节（Ni catalysts from laboratory investigations to chemical industry）。综上，本项目从重新构建高稳定镍铝催化剂入手，可为新型高抗积碳催化剂的研制、开发和工业应用提供理和技术支持。